Surface photovoltage (SPV) measurements were performed to investigate the optic-electrical properties in the electron beam irradiation semi-insulating GaAs (e-beam irradiation SI-GaAs) and semi-insulating GaAs (SI-GaAs). The signal intensity showed stronge. dependency on the frequency in the SI-GaAs than it did in the e-beam irradiation SI-GaAs. This result indicates that the number of the generated photo-carriers depends on the surface state. Also, the B region of the e-beam irradiation SI-GaAs found a weak signal. This result was explained by the surface and internal damage with e-beam irradiation.